Co-injection mixing method and apparatus

ABSTRACT

A method and device ( 10 ) for mixing polyurethane-forming liquid chemical components for the production of polyurethane foams, in which positive use is made of the turbulency and swirling action caused by the injection of pressurized jets of chemical components, in order to provide a methodology tending to improve the mixing processes by impingement and by the turbulency induced by a pressure drop in conventional self-cleaning apparatuses.

BACKGROUND OF THE INVENTION

This invention refers to a method and an apparatus for mixing liquidchemical components, in particular for the production of polyurethanefoams, in which positive use is made of the turbulency and swirlingaction caused by the injection of pressurized jets of chemicalcomponents, in order to provide a methodology tending to improve themixing processes by impingement and by the turbulency induced by apressure drop in conventional self-cleaning apparatuses.

PRIOR ART

In the production of polyurethane foams or moulded parts in rigid orflexible polyurethane material, two or more reactive chemicalcomponents, with a low boiling agent and/or additives, are mixed inspecial apparatuses according to known methods; the resulting reactivemixture is injected into a mould or poured on a substrate, where rapidlyreacts to form a polyurethane foam slabs or moulded pieces inpolyurethane material.

There are basically two mixing technologies, and namely: a first mixingmethod at low pressure, in the range of a few dozen bars or less,consisting in feeding the chemical components into a mixing chamberwhere they are thoroughly mixed by the mechanical action of a stirrerAccording to another mixing method, so-called by “impingement”, thechemical components are fed at high pressures, equivalent to or higherthan 100-150 bars (10-15 MPa) and separately injected into a mixingchamber at such high speed and kinetic energy, as to cause them to mixby impingement and turbulency of the resulting flows, after the jets ofthe individual components have crossed in a collision area.

This invention tends to improve this second type of technologySelf-cleaning type mixing apparatuses, normally also referred to ashigh-pressure mixing apparatuses or mixing heads have been used for someyears and are described in a number of prior documents, for example inU.S. Pat. Nos. 4,332,335, 4,477,191, 4,608,233 and 4,802,770.

The known high-pressure mixing apparatuses, require a separate injectionof the single components into a mixing chamber, through respectiveinjection nozzles, feeding the individual components at different highpressures, ranging for example from 100 to 300 bars (10 to 30 MPa) inorder to convert the high pressure energy with which each singlecomponent is fed, into a likewise high kinetic energy of the jets whichmix by impingement and by the turbulency induced by collision with oneanother and against the internal walls of the mixing chamber.

Even though the conventional high-pressure mixing apparatuses arestructurally simple and appreciated for several applications, thanks totheir good mixing and self-cleaning characteristics, they neverthelesspresent a number of limits and drawbacks due to the difficulty inimproving their efficiency, in particular in completing an intimatemixing of the chemical components, and in keeping a stoichiometric ratioat the beginning of the injection step.

In the past, attempts were made to obviate such limitation by adoptingparticular devices for unbalancing the pressures, or by making use ofmembers for throttling the outlet aperture of the mixing chamber,post-mixing chambers and/or devices, all of which tended to functionallyand structurally complicate the apparatus.

In particular, the mixing efficiency and the maintenance of the correctstoichiometric ratio in these apparatuses, are depending on the settingand control of the pressure at which each single component is fed;consequently, their chemical ratio is particularly critical especiallyduring initial and final mixing steps. In fact, the pressure settingoperations by means of the injection nozzles are critical also whencarried out by an expert operator, require good manual skills, take along time to be carried out, and normally call for preliminary tests forsetting up the entire installation. Moreover, whenever it is necessaryto mix chemical components which are highly viscous, or incompatiblewith one another from the standpoint of solubility and miscibility, suchas for example a lipophilic component and a hydrophilic component, ingeneral very high feed pressures must be used in order to obtain therequired mixing; consequently a greater energy consumption is requestedand greater structural and functional complications for the entirefeeding system for the components to the mixing apparatus.

Lastly, even though the mixing conditions can be improved by reducing,for example, the cross-sectional dimensions of the mixing chamber,because of the need to provide the necessary spacing and seals betweenthe single injection nozzles, and to limit its overall dimensions, inthe conventional high-pressure apparatuses it is not possible to fallbelow certain dimensional limits of the cross-sections of the mixingchambers, and consequently improve the mixing efficacy.

In general, therefore, in apparatuses of the aforementioned kind, it isdifficult and complicated to maintain sufficiently satisfactory mixingconditions in terms of proportioning, pressure and optimal mixing of thecomponents, especially upon variation in the flow rates, and duringtransient phenomena, as to produce a desired and complete reactionprocess, an adequate state of laminar flow ability of the mixture, andan adequate speed of polymerisation once the components have been mixedand injected into the cavity of a mould or distributed onto a substrate.

OBJECTS OF THE INVENTION

The main object of this invention is to provide a method for mixingreactive chemical components, in the production of polyurethane foamsand moulded articles in polyurethane material, which makes use, in a newand original way, of the turbulency and impingement mixing technology,by means of a self-cleaning mixing apparatus suitably modified toprovide an improved and easier control of the metering and mixingconditions, by using a comparatively less pressure drop than in theconventionally mixing apparatuses, thereby saving a substantial amountof energy and achieving a better mixing degree.

A further object of the invention is to provide a mixing method asdefined above, whereby it is possible to use a same pressure drop forinjecting the various components into an impingement and turbulencemixing chamber; this makes it possible to mix liquids having verydifficult or considerably different miscibility properties from oneanother, to obtain an intimate mixing and improved mixing degree.

The mixing method according to this invention can be used with anypolyurethane formulation, also containing suspended particles and/ordissolved or nucleated gases; advantageously, it can be used for mixinghighly viscous or mutually incompatible liquid components, in that itenables the mixing to be optimised by operating with low feedingpressure values, for example, 40-50% lower than those required by theconventional high-pressure mixing apparatuses.

All this results in greater operating reliability, considerable savingin terms of energy and management, and greater simplification of theapparatus, the entire feeding and metering system for the components,and the setting of the mixing conditions.

A further object is to provide a mixing apparatus particularly suitablefor carrying out the method indicated above, which constitutes analternative to the conventional high-pressure mixing apparatuses.

A still further object of the invention is to provide a high or mediumpressure mixing apparatus, by means of which it is possible to carry outa controlled metering and mixing of the various components, especiallyat the beginning and at the end of each mixing step, thanks to thepossibility of feeding all the components into the mixing chambersimultaneously and in a synchronised, quick and repetitive way, withoutrequiring excessively high pressures, by eliminating the so-calledpre-flow conditions which occur with the conventional apparatuses.

All this results in the greater structural and functional simplicity ofthe mixing apparatus, and greater simplicity in setting the injectionpressure, since the mixing is efficacious even with high percentages ofpressure losses along the feeding lines for the single components;greater efficacy is also achieved due to the possibility of using mixingchambers having such extremely reduced dimensions, as to promoteimproved mixing conditions.

A still further object of the invention is to provide a method and amixing apparatus of the type defined above, by means of which it ispossible to adjust the injecting conditions for the components into amixing chamber, simultaneously and conjointly for all the components,and in which the various jets which cross and collide or impinge withone another and/or against the walls of the mixing chamber, share incommon and present the same kinetic energy and turbulency, being subjectduring the injection to a same pressure drop.

A still further object is to provide a high and/or medium pressureself-cleaning mixing head or apparatus, by means of which it is possibleto use suitable outflow apertures for the jets towards the mixingchamber, of such kind as to achieve the conversion of the pressureenergy into kinetic energy and high turbulence for the mixing, therebypositively using the energy into the individual jets for mixing duringthe injection step.

What basically is distinguishing this invention, is the possibility ofeffectively flowing the chemical components in a jumbled condition undera same pressure value and partially mixing the various components bymeans of the swirling and turbulent motions of the chemical componentsas they are injected into the mixing chamber, and subsequentlycompleting the mixing by impingement.

A still further object of the invention is to provide a mixing apparatusof the type described above, whereby it is possible to simultaneouslyand also automatically adjust and setting a with a single operation thepressure drop for injection of the components into the mixing chamber,and change the total flow while easily maintaining mixing conditionssuitable for all the components.

BRIEF DESCRIPTION OF THE INVENTION

All the above is achievabieby means of a method for mixing liquidchemical components in the production of polyurethane foams or mouldedparts, as well as with a mixing device or a mixing apparatus.

More precisely, according to a first aspect of the invention, a mixingmethod for mixing chemically reactive liquid components has beenprovided, according to which at least a first and a second chemicalcomponents are fed under pressure conditions and mixed into a mixingchamber, and in which the resulting mixture is made to flow towards adelivery duct, comprising by the steps of:

-   -   feeding metered quantities of the chemical components into a        common pressure and feeding chamber in which the chemical        components are at a same common pressure and flow together        toward at least one injection restriction or orifice; and    -   co-injecting the jumbled chemical components into the mixing        chamber, through said at least one injection orifice to cause        intimate mixing by impingement and turbulency inside the mixing        chamber of the mixing device.

The chemical components are introduced or fed into the common pressureand feeding chamber from separate ports and flow in common and at apressure equal to or higher than 30 bars (3 MPa), preferably rangingfrom 40 to 160 bars (4 to 16 MPa), by appropriately adjusting the crosssectional areas of the injection restriction/s or orifice or orifices,in relation to the flow rates and characteristics of the chemicalcomponents to be mixed. By adjusting the cross sectional area of therestrictions or orifices the common pressure in the common pressure andfeeding chamber may be consequently adjusted. The pressure into thecommon pressure and feeding chamber in which the chemical components arefed and flowing brought together in a jumbled condition, is lower thanthe pressures required for feeding each single component to theinjectors of a conventional mixing apparatus, the injectors of whichmust be specifically and consequently adjusted for each singlecomponent; this will result in a more simple operation and possibilityto better adjust the mixing ratio.

For the scope of the present invention the “common pressure and feedingchamber” means that the chemical components are introduced separatelyinto the feeding chamber where they flow not yet mixed in an untidy orjumbled condition toward one or more restrictions or orifices where theyget in common a complete and very fine turbulence to be mixed.

According to a further feature of the invention a mixing device has beenprovided for mixing reactive chemical components, comprising;

-   -   a common pressure and feeding chamber;    -   a mixing chamber in fluid communication with the common pressure        and feeding chamber, and opening towards an outlet duct;    -   said common pressure and feeding chamber having inlet aperture        for separate feeding of the chemical components, and being        conformed for maintaining the chemical components, at a same        pressure and conveying them not yet mixed toward at least on        injection restriction or orifice;    -   said least one injection restriction or orifice being conformed        and arranged between the common pressure and feeding chamber and        the mixing chamber for co-injection of the chemical components        into the mixing chamber of the mixing device.

Preferably, a throttling member is provided for restricting thesectional flow area of the injection restriction or orifice, having ashaped fore end partially extending into an inlet aperture of the mixingchamber, the fore end of the flow throttling member and the inletaperture of the mixing chamber being conformed and disposed to form oneor more narrow injection restriction or orifices.

The flow throttling member is made axially movable and may be adjustablypositioned in order to change the cross sectional area of the flowpassage of the injection restriction or orifice or orifices, and toadjust the pressure inside the common pressure and feeding chamber, aswell as to change the pressure drop caused by the jet or jets of thejumbled chemical components, and consequently to adjust the kineticenergy and the shape of the eddies of the jets themselves; in this wayit is possible to change and adjust the mixing efficiency of theapparatus.

A cleaning member for cleaning the common pressure and feeding chamberand to allow a separate re-circulation of the chemical components, inthe form of a spool having a longitudinal bore, slides coaxially to andguides the flow throttling member. The cleaning member for the commonpressure and feeding chamber is movable between a backward position inwhich it opens the inlet apertures for the components, and a forwardposition in which it closes said inlet apertures and eject the residueof the chemical components which remain in the common pressure andfeeding chamber at the end of each mixing step, while simultaneouslyre-circulating each single component in a separate state.

In this connection, the bottom of the common pressure and feedingchamber and the fore end of the cleaning member present matching surfacemeans appropriately shaped to conform to each other to completely ejectthe residual chemical material when they are brought into contact.

The disposition and conformation of the common pressure and feedingchamber, the mixing chamber, the fore end of the throttling member, apost-mixing chamber wherever required, and an outlet duct for themixture, can be of any kind, provided they are suitable for the intendedpurpose.

For example, according to a preferential embodiment, the common pressureand feeding chamber and the mixing chamber are axially aligned; in thiscase, the flow throttling member can be adjusted and moved axiallybetween a backward position, for adjusting the cross sectional area ofthe injection orifice or orifices, and a forward position for closureand cleaning of the mixing chamber.

The axially aligned disposition of the common pressure and feedingchamber, the mixing chamber, and the longitudinally movable cleaningmembers, makes it possible to obtain a large-sized annularly-shapedjumbling chamber, and a mixing chamber of a considerably reduceddiameter, for example having a dimension of the cross sectional area ofan order smaller than that of a mixing chamber of conventional type;this helps to considerably improve the mixing which can thus take placeunder high turbulency conditions.

Since in the common pressure and feeding chamber the chemical componentscome only partially into contact with one another, and are consequentlyless subject to start the chemical reaction, the cleaning of the commonpressure and feeding chamber is therefore less critical.

It is nevertheless advantageous to contemplate the use of a slidingcleaning member in the common pressure and feeding chamber whichsimultaneously performs the squeezing out of the residual components andclose of the inlet apertures for the components; the cleaning member ispreferably connected to a hydraulic control cylinder which can beselectively operated with respect to a hydraulic control cylinder of thethrottling and cleaning member of the mixing chamber.

In addition to perform such function, the cleaning member of the commonpressure and feeding chamber can also carry out supplementary workingfunctions; for example, it can be provided with suitable longitudinal orcircumferential slots, or holes through which the single components canflow towards recirculation apertures or ducts comprising pressurecontrol valves.

A post-mixing chamber can be also provided downstream to the mixingchamber, in which the residual kinetic energy of the resulting mixtureis exploited to improve the mixing.

Furthermore, the mixing chamber can be disposed at right angle or form adifferent angle with the axis of the post-mixing chamber and/or with theaxis of the outlet duct, for example ranging from 30° to 150°.

The axis of the mixing chamber can be disposed on the same plane or on askew with respect to the axis of the post-mixing chamber and/or theoutlet duct.

According to another feature of the invention, the cleaning member forcleaning the mixing chamber is preferably in the form of a cylindricalpin ending at its fore end with a flat front surface, or with slanted ordifferently shaped flat surfaces, which may also be curved; in turn, atthe rear end of the mixing chamber some side walls may be provided forconveying the flow of components, disposed according to one or moreslanted flat surfaces; for example, said slanted surfaces may beprovided at the rear end of a bush member comprising the mixing chamber,which perfectly matches with corresponding slanted flat surfaces at thefore end of the movable cleaning member for the common pressure andfeeding chamber.

According to several preferential embodiments, the fore end of themovable cleaning member for the common pressure and feeding chamber andthe rear end of the bush member of the which corresponds to the fore endof the common pressure and feeding chamber, may present one or moreopposite matching surfaces variously disposed and slanted with respectto one another, and with respect to the longitudinal axis of the twochambers.

For example they may lie on slanted and radially oriented planes,angularly spaced apart from one another; in this way, when the flowthrottling member is in its backward position, at the inlet side of themixing chamber one or more narrow co-injection orifices for thecomponents are provided, in relation to the number of the slantedsurfaces at the bottom of the common pressure and feeding chamber. Forexample, the opposite ends of the common pressure and feeding chamberand of the corresponding cleaning rod member may have one slantedsurface only, lying a cross plane, or two V-shaped slanted surfaces, orfour or more slanted surfaces, in opposing pairs, slanting in oppositedirections, as described further on. The inclination of each surface,with respect to the longitudinal axis of the common pressure and feedingchamber, can be included in a wide range of values, preferably from 15°to 75°, greater or lesser, according to need.

In substitution of the flat surfaces, concave and/or convex and/ordifferently shaped surfaces can also be used.

According to a further feature of the invention, the cleaning member ofthe mixing chamber is in the form of an axially movable pin, the foreend of which may be provided with a flat front surface, disposed atright angle to the longitudinal axis of the mixing chamber, or with aconcave or differently shaped surfaces, depending on the axial or sidedisposition of the mixing chamber with respect to the outlet duct. Thebackwards position of the movable pin can be made axially adjustable soas to change the cross-sectional area of the injection orifice ororifices, and consequently the pressure existing in the common pressureand feeding chamber.

According to a further feature of the invention, the adjustment of theposition of the throttling and cleaning pin member of the mixingchamber, and consequently the adjustment of the cross sectional area ofthe injection restrictions or orifices, upon which the efficiency of themixing depends, can be carried out either manually, or in a controlledway by means of electromechanical or electrohydraulic actuatorsappropriately controlled by a processing unit; in this way it ispossible to optimise the pressure drop and, therefore, the efficiency ofthe mixing upon changes in the flow rate, physical conditions and numberof components to be mixed.

The apparatus according to the invention, in addition to permitting anefficient mixing of several liquid components, fed in stoichiometricratios by means of an accurate metering system, is also suitable for usewith the remote control of the parameters of a mixing process; this isparticularly advantageous whenever the production of the polyurethanematerial requires changes and modifications in the metered quantities,or the addition or elimination of one or more components between amixing phase and the next one, in order to give to the end productdifferent characteristics, or whenever it is necessary to modify thepressure conditions in the common pressure and feeding chamber, or forcompensating changes in viscosity of the liquid components to be mixed.

For the purpose of the present invention the term “common” when referredto the pressure and feeding chamber and the injection orifice ororifices of the apparatus, means that all the components are merely fedand introduced into a same chamber, and conjointly fed and injectedthrough a same common orifice.

The invention also makes it possible to obtain an outflow of the finalmixture with a desired laminar condition, so as to avoid formation ofsplashes or swirling at the outlet of the delivery duct.

BRIEF DESCRIPTION OF THE FIGURES

These and further features of the method and the apparatus according tothe invention, will be more clearly evident from the followingdescription with reference to the accompanying drawings, in which:

FIG. 1 shows a longitudinal cross-sectional view of a mixing apparatusaccording to a first preferential embodiment of the invention;

FIG. 2 shows a cross-sectional view along the line 2-2 of FIG. 1;

FIG. 3 shows an enlarged detail of FIG. 1, in perspective view;

FIG. 4 shows a cross-sectional view, in order to illustrate the closedcondition of the apparatus;

FIG. 5 shows an enlarged detail of FIG. 4;

FIG. 6 shows a cross-sectional view similar to that of FIG. 4, in theopen condition of the apparatus;

FIG. 7 shows an enlarged detail of FIG. 6;

FIG. 8 shows a cross-sectional view similar to that of FIGS. 4 and 6 inthe feeding condition;

FIG. 9 shows an enlarged detail of FIG. 8;

FIGS. 10, 11 and 12 show enlarged details similar to those of FIGS. 5, 7and 9 for a second preferential embodiment;

FIGS. 13, 14 and 15 show enlarged details similar to those of theprevious figures, for a third embodiment;

FIG. 16 shows a perspective view of the fore end of the cleaning memberof the common pressure and feeding chamber for the apparatus, accordingto the previous figs from 13 to 15;

FIGS. 17, 18 and 19 show enlarged details similar to those of FIGS. 5, 7and 9 in order to illustrate a further feature of the apparatusaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The general characteristics of the method and the apparatus according tothe invention, will be described hereunder with reference to the figuresfrom 1 to 9 which represent a first preferential embodiment.

As shown in the FIGS. 1 to 3, the apparatus comprises a body 10 made inone or several parts, having a hole 11 through which a spool member 12can reciprocate; the latter is in the form of a hollow rod memberconnected to the piston member 13 of a first hydraulic cylinder 13′, tobe moved between a forward position shown in FIG. 4, and a backwardposition shown in FIG. 8.

The fore end the hole 11 is provided with a bush 14 having a shaped rearend, which together with the fore end of the hollow spool member 12, inthe condition of FIGS. 1, 2, 3 and 9, forms a first chamber 15, alsoreferred to as common pressure and feeding chamber for chemicalcomponents, into which inlet apertures 16 and 17 for the introduction oftwo chemical components A and B open out at the ends of respectivefeeding ducts. The components A and B are delivered and fed in astoichiometrically proportioned ratio by respective positivedisplacement pumps, capable of supplying the required quantity, at apressure determined by their flowing through narrow co-injectionorifices which, from the common pressure and feeding chamber 15 open outinto a small mixing chamber 24. The components A and B are introducedinto the common pressure and feeding chamber, where they remain in ansubstantially unmixed or jumbled condition, at a same pressure, and fromwhere they are made to flow towards one or more co-injection orificesopening into the mixing chamber 24.

As previously mentioned, a stationary bush 14 is disposed at the foreend of the hole 11; the bush 14 defines a cylindrical mixing chamber 24having a cross-sectional area considerably smaller than that of thecommon pressure and feeding chamber 15, as well as smaller than that ofa mixing chamber of conventional type; for example its cross sectionaldimensions can be ten time smaller, compared to the dimensions of themixing chamber of conventional apparatuses.

In the example shown, the mixing chamber 24 in turn opens out into athird chamber 25A of greater diameter, also referred to as post-mixingchamber extending into an outlet duct 25B for delivering the resultingreactive mixture. As shown in FIG. 1, the chamber 25A and the outletduct 25B are disposed at an angle of 90° in respect to the mixingchamber 24; as an alternative, they can be disposed in the same plane orslant with respect to the longitudinal axis of the mixing chamber 24.

A cleaning member 26 longitudinally slides into the chamber 25A andalong the outlet duct 25B; the cleaning member 26 is connected to thepiston member 27 of a piston-cylinder arrangement of a hydraulic controlcylinder 28 to be moved between a backward position, in which it opensthe outlet of the mixing chamber towards the post-mixing chamber and theoutlet duct, and a forward position in which it ejects the residualmixture which remains in the chamber 25A and in the duct 25B at the endof each mixing and delivery step.

The apparatus also comprises a cleaning member for the mixing chamber24; this cleaning member consists of a pin member 29 connected to thepiston member 30 of a piston-cylinder arrangement of a respectivehydraulic control cylinder 30′, to be moved between a forward positionfor cleaning the mixing chamber 24, FIGS. 4 and 5, and a backwardposition for the communication of the jumbling chamber 15 with themixing chamber 24, FIGS. 6, 7, 8 and 9, in which the shaped fore end ofthe pin 29 and the correspondingly shaped rear end of the bush 14 defineone or more narrow restrictions or orifices for the co-injection intothe mixing chamber 24 of the chemical components A and B which flowunder pressure, in a substantially unmixed condition from separatefeeding ports to the orifices throughout the common pressure and feedingchamber 15, as explained further on.

The two control cylinders for the spool member 12 and the cleaning pin29 can be separate, or combined with each other into a single operatingunit in which the control piston of the piston-cylinder arrangement forthe cleaning pin 29 slides within a piston chamber made in the pistonmember of the control cylinder for the spool 12. In both cases, the twopiston chambers can be selectively connected, through suitable passages,to a common fluid source to be controlled in sequence, as shown in thevarious figures of the accompanying drawings.

The backward position of the cleaning pin 29, is adjustable and can bevaried by acting on a stop device 32 for the piston 30, the setting ofwhich can be carried out manually or by means of an electromechanical orelectro-hydraulic remote controlled device by an automatic systemcontrolled by a computer or by a programmable logic controller (PLC).

FIG. 3 of the accompanying drawings more clearly shows the main featureof the apparatus of FIG. 1, in a working condition to allow the feedingand introduction of the chemical components A and B into the commonpressure and feeding chamber 15 which is common to the variouscomponents, and for subsequent differentiated mixing steps. Inparticular performs a first feeding step for the introduction of thevarious components into the common pressure and feeding chamber 15, fromwhere the resulting jumbled components flow in a substantially unmixedor untidy condition, at a same common pressure, for example at apressure equivalent to or higher than 30 bars (3 MPa), towards themixing chamber 24 through one or more narrow co-injection orifices,capable of forming respective jets.

The starting step for introduction of the components into the commonpressure and feeding chamber 15 is followed by a first partial mixingwhich takes place in the jet or jets during the co-injection of thecomponents through each orifice 31, in which the pressure energyexisting in the common pressure and feeding chamber 15 is converted intoa kinetic energy, which gives rise to a partial turbulent mixing byturbulence along the jets themselves.

This is followed by a second mixing step by collision or impingementbetween opposite turbulent jets and/or collision against the walls ofthe mixing chamber 24, where the already partially mixed componentsundergo a thorough intimate mixing due to the intense turbulence causedby the high kinetic energy of the jets generated by the strong pressuredrop, in thin wall, of the injection orifice or orifices provided by theconfronting sharp edges of the bush 14 and tip of the pin 29.

As previously specified, the chemical components are to be introducedinto a common pressure and feeding chamber in which the components aresimply fed in common at a same pressure, to subsequently flow togethertoward restrictions or orifices where they are co-injected into a mixingchamber, where they undergo a complete intimate mixing, with greathydraulic efficiency, due to the sufficiently high kinetic energy of thejets as to generate a strong turbulence, which improves the mixingdegree.

The shapes, characteristics and dispositions of the common pressure andfeeding chamber, the mixing chamber, respective flow adjusting andcleaning members, may vary with respect to those shown, while stillremaining within the general scope of the invention.

According to a particular embodiment, shown in the figures from 1 to 3,the common pressure and feeding chamber 15 for the components is formedinto the longitudinal hole 11 of the body 10 of the apparatus, orassociated part thereof, and is delimited by the opposite shaped ends ofthe spool 12 and the bush 14 defining the bottom of the common pressureand feeding chamber 15, as shown; in particular, the pin 29 forthrottling the flow and cleaning the mixing chamber 24, which axiallyextends into the hole 11, contributes to form an annularly-shaped commonpressure and feeding chamber 15 between the opposite side surfaces.

More particularly, as shown in the enlarged details of FIG. 3 and FIG.9, the opposite ends of the spool member 12, and of the bush 14 aresimilarly V-shaped so as to provide two surfaces 12A, 12B slanting at45°, with respect to a plane passing through the longitudinal axis, andrespectively two similarly slanting surfaces 14A, 14B which arereciprocally matching with each other. In the example shown, thesurfaces 14A, 14B converge forward towards the mixing chamber, both inorder to form, with the front surfaces of the pin 29, the narroworifices 31 for the co-injection of the components A and B, and tofacilitate cleaning by the ejection of the residue of the chemicalmaterial which remains in the chamber 15 at the end of each operativestep. This can be achieved by bringing the movable spool member 12 closeto and urging the same against the end of the bush 14; however, anopposite or reversed disposition of the aforesaid surfaces, with respectto that shown, is not excluded.

Also in FIG. 3 it can be seen that the pin 29 in its backward positionextends within the common pressure and feeding chamber 15, with the foreend of said pin 29 partially penetrating, for a very brief length, intothe rear end of the mixing chamber 24; in particular, the fore end ofthe pin 29 comes to rest in a slightly backward position with respect tothe corner formed by the V-shaped surfaces at the rear end of the bush14, corresponding to the intersection line of the two slanting surfaces14A and 14B, to form two diametrically opposite narrow triangular slits31, only one of which is shown in FIG. 3, delimited by opposite sharpedges. Consequently, the chemical components into the common pressureand feeding chamber 15 are co-injected simultaneously into the mixingchamber 24, through the orifices 31 which gives rise to a sharp pressuredrop which in turn generates a strong turbulence in the jets along whicha partial mixing takes place, followed by a second intimate mixing byimpingement and related turbulency, between the jets and/or collisionagainst the walls of the mixing chamber itself. The resulting reactivemixture then flows from the mixing chamber 24 towards the post-mixingchamber 25A and/or into the outlet duct 25B.

From tests carried out, the solution of FIG. 3 proves to be highlyefficient in that the two chemical components A and B simply introducedin an unmixed condition into the common pressure and feeding chamber 15,flowed under pressure towards the orifices 31 through which they werepartially mixed in the jets as they were co-injected into the chamber24. By changing the aperture of the orifices 31, for example byadjusting the position of the pin 29, acting on an adjustable stopmember 32 for the piston 30 of the hydraulic control cylinder, it waspossible to change the pressure inside the common pressure and feedingchamber 15 and the pressure drop on the orifices 31; consequently thepressure drop and the kinetic energy of the jets may be changed in orderto obtain, in an extremely simple way, perfectly balanced co-injectionconditions for a better, more efficient and transient free mixing.

The chemical components A and B can be made to flow from storage tanks,along respective feeding lines, towards the common pressure and feedingchamber 15, at a same pressure, or at different pressure values,according to the required quantities and characteristics of thecomponents themselves; in any case, the various components will flow inthe common feeding chamber 15 at a same pressure resulting from thepressure drop caused by the injection orifices 31, and will consequentlybe co-injected at a same pressure, with jets of identical flow rate andspeed.

The figures from 4 to 9 schematically show the basic steps of theco-injected mixing method according to the invention, and the mainoperative conditions of the apparatus previously described withreference to the figures from 1 to 3.

In particular, the FIGS. 4 and 5 show the movable cleaning or spoolmember 12 of the common pressure and feeding chamber 15 and the cleaningpin 29 for the mixing chamber 24 in their fully forward condition, inwhich they close the inlet ports 16 and 17, and clean the commonpressure and feeding chamber 15 and the mixing chamber 24.

In this condition, the slanting surfaces 12A and 12B at the fore end ofthe movable spool member 12 are urged against the corresponding slantingsurfaces 14A and 14B at the rear end of the bush 14 of the mixingchamber, while the cleaning pin 29 extends totally into the hole of themixing chamber 24.

In order to start an operative cycle, from the conditions of FIGS. 4 and5, it is first necessary to move backwards the pin 29, stopping it inthe position shown in FIGS. 3, 6 and 7, in which it opens the orifices31 towards the mixing chamber 24.

In this condition, the spool member 12 is still fully forward againstthe bush 14 keeping closed the ports 16 and 17 for the inlet of thecomponents A and B, which can consequently be made to recirculate at apre-established pressure value, by means of appropriate outer valves,not shown, or in any other per se known way, towards their storagetanks.

Upon completion of the component recycling step, the subsequent stepcontemplates the backward movement of the spool 12 and the opening ofthe inlet ports or apertures 16 and 17 towards the common pressure andfeeding chamber 15 which is thus formed between the opposite end of themovable spool 12 and the bush 14.

The two components A and B are now introduced, in suitably meteredquantities, into the common pressure and feeding chamber 15 from wherethey flow together, in an unmixed and pressurised condition, towards andthrough the narrow orifices 31 so as to be co-injected into the mixingchamber 24; due to the high intrinsic turbulency of the jets, and due tothe energy generated by the same jets which impinge with one another inthe mixing chamber 24, the components A and B are thoroughly mixed, andthen flow into the post-mixing chamber 25A and into the outlet duct 25B.

Upon completion of the mixing and delivery steps, it is first necessaryto move the spool 12 forward so as to eject and squeeze out the residueof the component material remaining in the chamber 15 (FIGS. 6 and 7),and then move forward the cleaning pin 29 which in turn ejects theresidual mixture from the mixing chamber 24, towards the chamber 25A(FIG. 5), from where in turn it will be ejected by the rod 26 forcleaning the outlet duct 25B.

The FIGS. 10, 11 and 12 represent conditions identical to those of theprevious FIGS. 5, 7 and 9 for a different embodiment; in this case, themovable spool 12 and the fixed bush 14 are cut on a single slanted plane33 with respect to their longitudinal axes. Therefore, in this case, thecommon pressure and feeding chamber 15 will be defined by the slantedsurfaces 33A, 33B which extend parallel to each other, forming an angleof 45°, or an angle ranging from 15° to 75° with respect to thelongitudinal axis of the chamber 15. In these case, the same referencenumbers of the previous figures have been used to indicate similar orequivalent parts.

The operative method of the apparatus of FIGS. 10-12 is wholly identicalto that of the apparatus of the previous figures, to which it isconsequently referred.

The FIGS. 13, 14, 15 and 16 show a third embodiment substantiallysimilar to that of the previous figures, which has been modified in theshape of the opposite ends of the spool member 12 and of the fixed bush14 defining the mixing chamber, to form four jets.

In this case, the common pressure and feeding chamber 15 can be providedwith four inlet ports for four components; consequently, both the tip ofthe spool member 12 and the rear end of the fixed bush 14 will beprovided with crossed V-shaped cuts, or with V-shaped slanting surfaces12′, 12″ angularly slanting and circumferentially spaced apart from eachother, as for example shown at the fore end of the spool member 12 inthe perspective view of FIG. 16.

Here too, the solution of FIGS. 13-16 will operate in a wholly identicalway to that described for the previous examples, with the soledifference that now four narrow co-injection orifices, in oppositepairs, are formed, together with the corresponding formation of fourjets which will be injected into the mixing chamber 24.

The same reference numbers have been used also in FIGS. 13, 14, 15 and16 to indicate parts similar or equivalent to the previous examples.

FIGS. 17, 18 and 19 show a fourth embodiment similar to that of FIGS. 5,7 and 9 which has been modified to obtain an internal recirculation ofthe components; in the previous cases, the recirculation of thecomponents could be carried out outside the mixing apparatus, by meansof an appropriate valve assembly, in a per se known way.

Conversely, in the case of FIGS. 17, 18 and 19, the recirculation iscarried out inside the apparatus, for example by providing in a per seknown manner a recycling port 34 and 35 in correspondence with eachinlet port 16 and 17, and by providing the movable spool 12 withlongitudinal slots 36 and 37, to flow each component between inlet ports16, 17 and recirculation ports 34, 35.

With the exception of the recirculation step, the apparatus of theexample shown in FIGS. 17, 18 and 19, again operates in an identical wayto that of the previous examples. Therefore, the same reference numbershave again been used to indicate similar or equivalent parts.

Figures from 1 to 19 show some of the numerous possible embodiments ofmixing apparatuses suitable for carrying out the co-injection methodaccording to the invention; it is obvious however that other solutionsare possible within the scope of this invention.

For example, the post-mixing chamber 25A and the delivery duct 25B ofFIG. 1 could also be omitted, in which case it would be necessary tosuitably extend the length of the mixing chamber 24 to prevent theoutflow of a turbulent jet.

It would also be possible to contemplate a different disposition andorientation of the mixing chamber 24 with respect to the chamber 25A andto the outlet duct 25B. In the case of FIG. 1, the longitudinal axis ofthe mixing chamber 24 is at right angles with and on the same plane asthe longitudinal axis of the chamber 25A; however, other dispositionsare possible in which the axis of the mixing chamber 24 is disposed in adifferent plane, or to one side of the axis of the chamber 25A, or anangularly slanted disposition of the chamber 24, with respect to thechamber 25, towards the cleaning pin 29 so that the stream of themixture flowing out of the mixing chamber is in counter-current, or inthe opposite direction to the flow of the mixture in the outlet duct25B.

In this case, the tip end of the pin 29 would be cut on a bias withrespect to its longitudinal axis and the bottom end of the commonpressure and feeding chamber would be flat or V-shaped.

From what has been described and shown, it will be clear that what isprovided is a procedure and a new self-cleaning apparatus for mixingreactive chemical components in the production of rigid or flexiblepolyurethane foams, or moulded parts in polyurethane material, whichmake use in a new and original way of the principle of mixing byturbulency and collision or impingement; in fact, unlike theconventional apparatuses, where the components are injected separatelyat high kinetic energy into the mixing chamber and where their mixingcan start only after the single jets of the components have crossed andimpinged with one another, according to this invention, thanks to theuse of a common pressure and feeding chamber shared by the variouschemical components to be mixed, the mixing starts during the sameco-injection of the components from the narrow orifices which open outinto the mixing chamber, due to the swirling motion of the jets, and bysuccessive impingement, thereby achieving an efficient final mixing.

Moreover, the pressure of the various jets can be controlledsimultaneously by operating a single adjusting member consisting of thesame cleaning pin 29 for the mixing chamber. Lastly, the mixing chambercan have a cross-sectional area considerably smaller than that of aconventional apparatus of the same capacity, thereby further increasingthe efficacy of the mixing.

It is understood however that what has been described and shown in thevarious figures has been given purely by way of example in order toillustrate the invention, and that other modifications and variationsmay be made without thereby deviating from the scope of what is claimedherein.

1. A method for mixing chemically reactive liquid chemical components(A, B) into a mixing device (10), for production of polyurethane foamsand moulded parts, in which metered quantities of a first (A) and atleast a second (B) chemically reactive components are fed under pressureconditions into a first chamber (15) and made to flow into a secondchamber (24) through at least one injection orifice (31), said methodcomprising: providing an annularly shaped common pressure and feedingchamber (15); feeding metered quantities of the chemical components (A,B) into the annularly shaped common pressure and feeding chamber (15)common to the chemical components (A, B), provided by said first chamberof the mixing device (10) maintaining the chemical components (A, B)inside the feeding chamber (15) in an unmixed state and at a samepressure condition, while they are flowing toward the at least onerestriction or orifice (31); co-injecting the unmixed chemicalcomponents (A, B) feed in common, into a mixing chamber (24) provided bysaid second chamber (24), through said least one injection orifice (31);and causing a first mixing of the co-injected chemical components (A,B)by turbulency during co-injection, and a second intimate mixing byimpingement and turbulency into the mixing chamber (24) of the mixingdevice (16).
 2. The method according to claim 1, comprising theadditional step of pre-mixing the chemical components by the turbulencyof a jet during the co-injection.
 3. The method according to claim 1,wherein the chemical components (A, B) are co-injected into the mixingchamber (24) provided by said second chamber, while maintaining in thecommon pressure and feeding chamber (15) a pressure equal to or higherthan 30 bars (3,0 Mpa ).
 4. The method according to claim 3, wherein thepressure in the common pressure and feeding chamber (15) is ranging from40 to 160 bars (4 to 16 Mpa)
 5. The method according to claim 1, inwhich the mixing second chamber (24) is provided with a rear open end,and a flow throttling member (29) having a shaped end axially protrudinginto the rear opening of the mixing chamber (24) to provide said atleast one injection orifice (31), wherein the pressure of the common fedchemical components (A, B) in the common pressure and feeding chamber(15) is changed by adjusting the axial position of the throttling member(15) shaped end in respect to the rear opening of the mixing chamber(24).
 6. The method according to claim 1, comprising the step ofpost-mixing of the resulting mixture outcoming from the mixing secondchamber (24).
 7. A mixing device for mixing reactive chemical components(A, B), having: a mixing chamber (24) and an outlet duct (25B);characterized by comprising: an annularly shaped common pressure andfeeding chamber (15) in fluid communication with said mixing chamber(24); said common pressure and feeding chamber (15) having inletapertures (16, 17) for separate feeding of the chemical components (A,B), and being conformed for maintaining the flowing of the chemicalcomponents (A, B), in common, at a same pressure and in unmixed state;at least one injection orifice (31), conformed and arranged forco-injection of the chemical components (A, B), from the common pressureand feeding chamber (15) into the mixing chamber (24) of the mixingdevice (10); and a throttling member (29) for the at least one injectionorifice (31) coaxially arranged inside the feeding chamber (15), saidthrottling member (29) having a fore end partially protruding into aninlet aperture of the mixing chamber (24), and conformed to provide saidat least one injection restriction or orifice (31) between oppositeedges of inlet aperture of the mixing chamber (24) and the fore end ofthrottling member (29).
 8. The mixing device according to claim 7,wherein the opposite confronting faces at the bottom of the feedingchamber (15) and of the fore end of the throttling member (29) areprovided with shaped surfaces defining said at least one injectionrestriction or orifice (31).
 9. The mixing device according to claim 7,wherein the throttling member (29) is axially adjustable in respect tothe inlet aperture of the mixing chamber (24).
 10. The mixing deviceaccording to claim 7 comprising a cleaning member (29) axially movablewithin the mixing chamber (24).
 11. The mixing apparatus according toclaim 10, wherein the cleaning member (29) is consisting of a throttlingmember (29).
 12. The mixing device according to claim 11, wherein thecleaning and throttling member (29) is movable between an advanced and aretracted position in respect to the mixing chamber (24), and means foradjusting the axial position of the throttling member (29) and to changethe sectional area of the injection orifice (31) at the retractedposition of the throttling member (29).
 13. The mixing device accordingto claim 7, wherein the common pressure and feeding chamber (15) and themixing chamber (24) are axially aligned.
 14. The mixing device accordingto claim 7, wherein the mixing chamber (24) has a cross sectional areasmaller than that of the common pressure and feeding chamber (15). 15.The mixing device according to claim 7, wherein the mixing chamber (24)opens out into a post-mixing chamber (25A).
 16. The mixing deviceaccording to claim 15, wherein the post-mixing chamber (25A) isangularly oriented, with respect to the mixing chamber (24).
 17. A Themixing device according to claim 16 wherein the post-mixing chamber(25A) is arranged in a different plane.
 18. The mixing device accordingto claim 15, wherein the post-mixing chamber (25) has a cross sectionalarea larger than that of the mixing chamber (24).
 19. The mixing deviceaccording to claim 15, wherein the axis of the post-mixing chamber (25A)forms an angle ranging from 45° to 150° with the axis of the mixingchamber (24).
 20. The mixing device according to claim 7, comprising acleaning member (12), axially movable within the common pressure andfeeding chamber (15).
 21. The mixing device according to claim 20wherein the feeding chamber (15) is provided with axially spaced apartinlet and outlet apertures (16, 34; 17, 35) for feeding and recycling ofthe chemical components (A, B), the cleaning member (12) for the commonpressure and feeding chamber (15) comprising a spool member conformedfor opening and closing said inlet apertures (16, 17), respectively forconnecting said inlet apertures (16, 17) with the outlet apertures (34,35) for recirculation of the chemical components (A, B).
 22. The mixingdevice according to claim 21, wherein said spool member (12) comprisesre-circulation slots (36, 37).
 23. The mixing device according to claim20, wherein the cleaning member (12) for the common pressure and feedingchamber (15) consists of a hollow spool member (12) having alongitudinal bore, and wherein a throttling member (29) is providedcomprising an elongated pin member axially movable within the bore ofsaid spool (12).
 24. The mixing device according to claim 23, whereinthe spool member (12) for cleaning common pressure and feeding chamber(15) and the cleaning member (29) for the mixing chamber (24), areconnected to selectively operable hydraulic control actuators (13, 30).25. A mixing device according to claim 7, comprising; a body (10) havingan elongated hole and a common pressure and feeding chamber (15) for thechemical components (A, B) in said elongated hole, said common pressureand feeding chamber (15) having inlet apertures for chemical components;a bush member (14) at the fore end of said elongated bole, said bushmember (14) defining the mixing chamber (24); and; a spool member (12)axially sliding in said feeding chamber (15), operatively connected to afirst hydraulic control cylinder (13); the opposite ends of the bushmember (14) and the spool member (12) having reciprocally matchingfacing surfaces (12A, 12B; 14A, 14B; 33A, 33B).
 26. The mixing deviceaccording to claim 25 wherein the opposite ends of the bush member (14)and the spool member (12) have at least one, facing surface parallelarranged to a same slanting plane.
 27. The mixing device according toclaim 26, wherein said slanting plane forms an angle ranging from 15° to75° with respect to the longitudinal axis of a jumbling chamber (15).28. A self cleaning mixing apparatus for mixing at least first andsecond reactive polyurethane-forming chemical components, comprising: abody (10) having a first longitudinal bore (11) wherein a commonpressure and feeding chamber (15); for feeding in common the chemicalcomponents (A, B) and a mixing chamber (24) are provided in said firstlongitudinal bore (11), the mixing chamber (24) having a rear open endprovided with slanted shaped edges; at least first and second inletapertures (16, 17) for the chemical components (A, B), opening into saidfeeding chamber (15); a first cleaning and spool member (12) for thecommon pressure and feeding chamber (15) slidably received within saidfirst longitudinal bore (11) to move between a closed and an opencondition of the inlet apertures (16, 17) of the feeding chamber (15);wherein a second cleaning member (29) for the mixing chamber (24) isslidably received and protrudes from a longitudinal bore in said spoolmember (12), said second cleaning member (29) being movable between anadvanced and a retracted position in respect to the mixing chamber (24);and wherein at least one injection restriction or orifice (31) isperformed between the shaped edges at the rear end of mixing chamber(24) and front shaped edges of the second cleaning member (29) forco-injection of the not yet mixed chemical components from the feedingchamber (15) into the mixing chamber (24) of the mixing apparatus. 29.The self-cleaning apparatus according to claim 28, comprising first andsecond hydraulic actuators (13, 13′; 30, 30′) operatively connected tosaid first and second cleaning members (12, 29) and selectivelyconnectable a fluid source.
 30. The self-cleaning apparatus according toclaim 28, wherein said hydraulic actuators comprises first and secondcylinder-piston arrangements (13, 13′; 30, 30′), each of the saidcylinder-piston arrangement comprising a piston chamber (13′, 30′) and apiston member (13, 30), and wherein the piston chamber (30′) of thesecond cylinder-piston arrangement (30, 30′) is provided in the pistonmember (13) of said first cylinder-piston arrangement (13, 13′).
 31. Theself-cleaning apparatus according to claim 28 comprising a throttlingdevice for throttling the injection orifice (31), said throttling devicecomprising the second cleaning member (29) for the mixing chatter (24)and adjustable stop means (32) at the retracted position of the secondcleaning member (29).